Troubleshooting 'lqr' Command Failures in MATLAB: Stabilization and Optimal Gain Issues

The 'lqr' command failed to stabilize the plant or find an optimal feedback gain. To remedy this problem:

1. Make sure that all unstable poles of A are controllable through B (use MINREAL to check)
2. Modify the weights Q and R to make [Q N;N' R] positive definite (use EIG to check positivity).
3. Increase the value of the regularization parameter, if applicable.
4. Consider using a different control design method, such as pole placement or H-infinity control.
5. Check for errors in the system model or measurement data.
6. Consult with an expert in control theory for further assistance.